Central meridian, each meridian 90° from central meridian, and the Equator are straight lines. Other meridians and parallels are complex curves, concave toward the central meridian and the nearest pole, respectively.
Poles: Points along the central meridian
Symmetry: About any straight meridian or the Equator

Scale

True along the central meridian and along any straight line perpendicular to the central meridian
Increases with distance from the central meridian, along a direction parallel to the central meridian

Distortion

Function of the distance from the central meridian. No distortion occurs along the central meridian, but there is both area and local shape distortion elsewhere.

Other features

Conceptually projected onto a cylinder tangent to the globe at the central meridian
Can be compressed north-south to provide a Transverse Equirectangular projection, but rarely done

Usage

Topographic mapping (ellipsoidal form) of British Isles before the 1920s; replaced by the Transverse Mercator
Topographic mapping of a few countries currently

Origin

Developed by César François Cassini de Thury (1714-1784) for topographic mapping of France in the middle 18th century

Description adapted from J.P. Snyder and P.M. Voxland, An Album of Map Projections, U.S. Geological Survey Professional Paper 1453. United States Government Printing Office: 1989.